Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $61.53   9.276%   $67.2375   $67.24   $67.25   $67.20  
  Purchase #2 $97.95   4.847%   $102.6976   $102.70   $102.70   $102.70  
  Purchase #3 $50.64   12.130%   $56.7826   $56.78   $56.80   $56.80  
  Purchase #4 $146.51   7.517%   $157.5232   $157.52   $157.50   $157.50  
  Purchase #5 $43.42   4.210%   $45.248   $45.25   $45.25   $45.20  
  Purchase #6 $13.31   3.862%   $13.824   $13.82   $13.80   $13.80  
  Purchase #7 $125.62   10.792%   $139.1769   $139.18   $139.20   $139.20  
  7 purchase totals = $538.98       $582.4898   $582.49   $582.50   $582.40